Serious doubts remain that Afghanistan will be able to recover nearly $1bn (£631.4m)frittered away on disastrous business ventures and now worthless Dubai properties by the disgraced former owners of Kabul Bank, the country's finance minister has said.

Omar Zakhilwal's admission that "almost everyone" within the international community remained concerned about efforts to undo the financial damage caused by one of the worst bank scandals in history came despite the International Monetary Fund giving the green light to the government's asset recovery plans.

The decision, taken by the IMF's board on Monday night, to reinstate its programme in Afghanistan brought to an end a bitter 18-month dispute and reopened the doors to vital foreign cash donations, on which the country is utterly reliant.

Major donors, including the Department for International Development and the World Bank, had suspended funds for almost a year while the IMF remained dissatisfied with the response to the banking crisis.

Zakhilwal said the decision marked the "end of a difficult ordeal we had with our donors" that would allow him to focus on recovering missing assets to repay the $825m (£520bn) Afghanistan was forced to borrow from its own foreign reserves last year to prop up the fraud-tainted bank.

But so far only $75m in cash has been recovered, an amount almost wiped out by additional losses uncovered in recent months by international auditors.

Officials say that in addition to the small amount recovered so far, assets worth $150m have been surrendered while an additional $250m of assets have been identified.

Zakhilwal said he expected $600m would ultimately be recovered.

"We know the international community has its doubts but we will prove them wrong," he said.

His target is ambitious figure given the extraordinary complexity of the task in a country severely lacking in the necessary legal expertise.

Kabul Bank's own paperwork often gives no information as to who took out money. Many borrowers are identified as either "unknown" or, in some cases, "Kaka jan", an Afghan term of endearment meaning "dear uncle".

There are also doubts whether the Dubai villas on the man-made Palm Jumeirah peninsula bought with proceeds from the scandal will ever be seized. It is feared that many are mired in negative equity and therefore worthless to Kabul Bank's receivers.

Also, there are concerns that pressure may now come off the most well-connected beneficiaries of the bank's interest-free largesse, not least as the loans often benefited some of the most important people in the country, including Mahmoud Karzai, a brother of the Afghan president.

The restrictions on former Kabul Bank chairman Sherkhan Farnood, and former chief executive Khalilullah Ferozi, already appear to have eased. They were arrested and imprisoned this summer, but recently have moved to a day release schedule, and have even been seen eating in Kabul's only five-star hotel.

In June Ferozi told the Guardian that he would not co-operate on asset recovery if he was convicted of a crime.

And in an email sent at about the same time, Farnood threatened to reveal "many cases and documents regarding Mr Mahmood Karzai and Karzai's family and their businesses".

"Mr Hamid Karzai [knew] about these problems and deliberately did not assist to resolve, I believe he has political and financial interest," he wrote.